Fluoride contamination in groundwater prevents several hundred million people worldwide from accessing clean water.Among defluoridation technologies, a fixed-bed sorption process is considered to be the most suitable method in rural and remote locations. However, the currently used fluoride selective sorbents, such as hydroxyapatite (i.e., bone char), activated alumina, and other metal oxide based-sorbents exhibit very low sorption capacity, especially at near neutral to mildly alkaline pH (6.5-8.5) of typical fluoride-contaminated groundwater. The present study provides a novel reusable hybrid nanosorbent capable of simple regeneration that can treat fluoride-contaminated groundwater across the relevant pH range. The system is essentially a packed-bed of macroporous strong acid cation exchange resin (e.g., Purolite C145) preloaded in Al3+ form. Once the cation exchange takes place (i.e., a hardness cation such as Ca2+ or Mg2+, usually present in groundwater, displaces the Al3+ ions from the cation exchanger), the aluminium ions undergo hydrolysis reaction and form hydrated aluminium (hydr)oxide particles that precipitate onto the gel and/or within the pore phase of the macroporous cation exchanger.Fluoride is then removed from aqueous phase through Lewis acid-base interactions with freshly precipitated HAlO particles. Moreover, protons produced during the aluminium hydrolysis can promote acidic condition inside the resin phase resulting in higher sorption affinity between HAlO and fluoride ions, with effluent at pH 6. From the experimental column runs, the hybrid material can remove fluoride below WHO recommended levels (1.5 mg/L) for more than 500 bed volumes (BV) of alkaline influent (5 mg F/L, pH 8.0) and is stable for more than five exhaustion-regeneration cycles, over 12.5x greater performance than activated alumina (40 BV). The exhausted resins can be regenerated by passing nearly stoichiometric amounts of aluminium, based on the resin exchange capacity, using diluted 2% AlCl3 solution.The element maps of the exhausted resin from SEM/ EDX confirm that both aluminum and fluoride were well dispersed throughout the resin.

Enhanced defluoridation using hybrid polymeric cation exchangers in Al<sup>3+</sup> form containing hydrated Al(III) oxide nanoparticles

247th National Meeting (2014)

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Enhanced defluoridation using hybrid polymeric cation exchangers in Al3+ form containing hydrated Al(III) oxide nanoparticles

Enhanced defluoridation using hybrid polymeric cation exchangers in Al³⁺ form containing hydrated Al(III) oxide nanoparticles